Paul Green, of School of Rock fame, has a raspy voice and man-child ways that make his cinematic doppelganger Jack Black look like a naïf. He bounds about Todd Rundgren’s old Utopia Studios, reading inspiring notes from his iPhone or leaping onto the stage to thrash out some licks to the music he’s rehearsing a roomful of local kids through — Pink Floyd’s “The Wall” — with a minimum of self-consciousness. He’s as rock ‘n roll, in his jeans and black shirt, slight paunch and oft-noted ass crack bared, as anything bad ass not seen on a record cover or in some publicist’s promo package. He’s as rock ‘n roll, to put it another way, as Woodstock’s ever been.